Ligand-Induced Conformational Rearrangements Promote Interaction between the Escherichia coli Enterobactin Biosynthetic Proteins EntE and EntB† †This work was supported by Discovery Grant 341983-07 from the Natural Sciences and Engi- neering Research Council of Canada to PDP Sofia Khalil and Peter D. Pawelek* Department of Chemistry and Biochemistry, Concordia University, 7141 Sherbrooke St., W., Montreal, Quebec, Canada, H4B 1R6 *Correspondence should be addressed to: Peter D. Pawelek, Tel: 514-848-2424 ext. 3118; Fax: 514-848-2868; E-mail:
[email protected] Running title: Efficient EntE-EntB interaction requires 2,3-dihydroxybenzoic acid Abbreviations The following abbreviations are used in this manuscript: 2,3-DHB: 2,3-dihydroxybenzoic acid; 2,5-DHB: 2,5-dihydroxybenzoic acid; 3,5-DHB: 3,5-dihydroxybenzoic acid; AMP: adenosine monophosphate; ArCP: aryl carrier protein; ATP: adenosine triphosphate; CD: circular dichro- ism; DTT: dithiothreitol; FRET: fluorescence resonance energy transfer; H6-EntB: purified, re- combinant hexahistidine-tagged E. coli EntB; H6-EntE: purified, recombinant hexahistidine- tagged E. coli EntE; ICL: isochorismate lyase; ITC: isothermal titration calorimetry; NRPS: non- ribosomal peptide synthesis; PDB: Protein Data Bank; RMSD: root mean square deviation; SDS- PAGE: sodium dodecyl sulfate polyacrylamide gel electrophoresis; TCEP: tris(2- carboxyethyl)phosphine. 2 Abstract Siderophores are small-molecule iron chelators that many bacteria synthesize and secrete in or- der to survive in iron-depleted environments. Biosynthesis of enterobactin, the E. coli catecho- late siderophore, requires adenylation of 2,3-DHB by the cytoplasmic enzyme EntE. The DHB- AMP product is then transferred to the active site of holo-EntB subsequent to formation of an EntE-EntB complex.